The present invention relates to the art of workpiece ejectors for presses and, more particularly, to an improved mechanical-hydraulic ejector system for presses.
It is of course well known to provide presses with workpiece ejectors operable to separate a workpiece from press tooling following the forming or other work performed on the workpiece while interposed between the tooling. Among the ejector systems heretofore provided for this purpose are mechanical-hydraulic arrangements such as that shown in my U.S. Pat. No. 4,068,520 wherein a workpiece ejecting member is hydraulically displaced in an ejecting direction during return movement of a press slide by means of hydraulic pistons which are actuated by cams carried by the press slide. The use of cams displaced by the press slide for actuating the hydraulic pistons advantageously enables achieving displacement of the ejector member with desired acceleration and deceleration characteristics. However, such an ejector arrangement requires accurate machining of the cams for this purpose, and accurate positioning of the cams relative to the hydraulic pistons to achieve the desired length of the ejector member stroke and timing thereof with respect to slide movement. Accordingly, the arrangement is undesirably expensive to manufacture and incorporate in the press structure and, additionally, requires adjustment of the cam members relative to the hydraulic pistons each time the press shut height is adjusted. The latter requirement results in considerable down time and maintenance costs in connection with such shut height adjusting. Moreover, cams having different profiles are required in order to vary the ejector stroke length to enable the use of different tooling sets with the press. This requirement increases costs with respect to the ejector mechanism or, if different cams are not provided, limits versatility of the ejector mechanism and thus use of the press to tooling which the ejector mechanism can properly function.
Another mechanical-hydraulic ejector arrangement heretofore provided is disclosed in U.S. Pat. No. 3,157,111 to Andersen. In the arrangement disclosed in the latter patent, the displacement of hydraulic fluid relative to an ejecting piston is achieved by means of a piston and cylinder assembly connected between the press slide and frame. The cylinder provides a fluid chamber into and from which hydraulic fluid is displaced in response to reciprocation of the press slide, and the flow of fluid between the chamber and the ejector piston and a fluid reservoir is controlled by a shutoff valve and a pressure regulating valve, both of which are cam actuated in response to reciprocation of the slide relative to the press frame. The shutoff valve provides for fluid flow to the ejector piston during a short period of the return stroke of the slide, and the pressure regulating valve provides for such fluid flow to be at a constant pressure. Ejector systems of this character are undesirably expensive as a result of the cams, valves and complex flow line arrangements required to achieve the desired patterns of fluid flow. Further, the cam for the shutoff valve must be adjusted each time the slide shut height is changed and must be adjusted to obtain and maintain the desired timing of the ejector actuation. These adjustment requirements result in increased down time and maintenance costs with respect to press operation. Still further, the control of fluid flow by a shutoff valve and pressure regulating valve result in flow characteristics in the system which generate undesirably high temperatures, sudden pressures and flow direction changes which are detrimental to the component parts of the system, and the sudden and high velocity displacement of the ejector piston to the ejecting position thereof. Such displacement of the ejector piston can result in propelling a workpiece from the tooling as opposed to merely achieving release of the workpiece from the tooling.